If you remove a website from the about:newtab page then try to drag a tab to a tile on the page. Otherwise you can clear (reset) the browser.newtabpage.blocked pref on the about:config page (this pref stores hashes of blocked websites).

You can change the order of the boxes on the about:newtab page and drag an item to a different tile to pin it to that position or you can remove a website by clicking the close X to block that URL. You can drag a bookmark or history item from the sidebar and drop it in a tile on the about:newtab page to pin this item and have your own favorites sites present.

Changes made manually on the about:newtab page are stored in prefs that you can find on the about:config page.

• browser.newtabpage.pinned stores websites that you have pinned to a tile.
• browser.newtabpage.blocked stores websites that you have removed by clicking the X button in a tile.

You can open the about:config page via the location/address bar. You can accept the warning and click "I'll be careful" to continue.

• http://kb.mozillazine.org/about:config

I attempted to drag a tab to the new tab window but does not behave/accpet it as a new Tile.

Regarding 'browser.newtabpage.blocked' on about;config, there is no such configuration entry with that name.

Does anyone else know what to do ?

For reference, here are screenshots is what happens when I attempt the above

Hi, try bookmarking the site you want to add. Now open bookmarks in the sidebar (Ctrl+B) and drag the bookmark onto a thumbnail on the New Tab page.

Hi Scribe

That behavior causes the website in question to load in the new tab, but alas it does not add it as a new tile.

Anyone else know how to fix this ?

Try to drag the "Site Identity Button" (control center 'i' button) at the left end of the location/address bar to a tile to pin the website.

Also make sure that you aren't in permanent Private Browsing mode (Always use Private Browsing mode; Never Remember History).